Direct reading hygrometer



April 5, 1938. J. c. BARNES 2,113,072

DIRECT READING HYGROMETER Filed Sept. 16, 1936 T/v: HUMIDITY COMFOETZONE l N VEN 70 0a mes Carzurz'yfiz .Ba 7' nes ATTaAM EY UNITED STATESPATIENT OFFIQE DIRECT READING .HYGROMETER James Cartwright Barnes,Toronto, Ontario,

Canada Application September 16, 1936, Serial No. 100.992

In Canada September 19, 19,35

3 Claims. (01. '73.-338) My invention relates to what is commonlyassociated parts necessary for the operation of known as wet and drybulb hygrometer and the instrument.

is particularly directed towards providing an in- Fig. 2 is a front viewof the indicator arm. strument by means of which it is possible to readFi 3 is a front view of the L-shaped member.

5 directly the percent relative humidity of the at- The instrumentillustrated in the drawing COm- 5' mosphere without the necessity ofreferring to prises a panel l2 on which are mounted two simiseparategraphs or tables. larly calibrated thermometers I and 2. It is The mostcommon of the wet and dry bulb essential from the viewpoint of accuracythat hygrometers comprises two thermometers, simih y a e Ca ated sSimilarly as p s b and larly calibrated, fixed side by side on a commonlocated on a common base line in such a manner 10 base line. The bulb ofthe dry bulb thermomthat each calibration mark of the scales is dieteris exposed to the atmosphere while the bulb re t y opp s t th c r p d atn of the wet bulb thermometer is enclosed in the k of the h r h r. In hr pect upper end of a piece of absorbent cloth, such as I prefer o m unteach thermometer on a movl k, th lower end f th th being 1 able base insuch a manner that each thermoml5 mersed in a vessel of water maintainedat sub- 9591" y be p t y v e n an upward OI tantia ny atmospherictemperature Water is downward direction as shall hereinafter beexabsorbed by the absorbent cloth with the result s As a furtherfeature, also from the that the cloth enclosing the bulb of that ther-Viewpoint of accuracy, it is desirable that the 2O mometer is keptsaturated. At the same time thermometers Should be of the non'magnifyingwater is continually evaporating from the absorbstem typeent cloth witha corresponding absorption of heat The bulb M of thelthermometer exposedso that the Water evaporated f the cloth to the atmosphere while thebulb 15 of the ther- Closing the bulb of the bulb thermometer mometer 2is enclosed in the upper end of the maintains that bulb cooler thanatmospheric absorbelilt cloth the lower end P which is 25 temperaturethus Causing a difference in the mersed in the water H confined 1n thevessel I0.

perature reading between the two thermometers. Th arm 4 of the L',shapedmember and It will be apparent that the rate of evaporation folmmg pajrtthereof 18 movably q; on

is dependent on the relative humidity of the atthe 5 While the 1 6extends Over the dry mosphere which is indicated by a greater or lesserbulbn mtarmomemr I Suck} mantle? a the difference in the temperaturereading of the two onfice 7 bored m sald arm 6 1S dlrectly thermometers.This difference in the tempera- 3x lapproxlmate to the stem of the ther'35 E2 5??? fg fizi g zgag ggig gi :3 3? The orifice provided in the Lshaped member 35 tables Supplied with the instrument 3 forms the pivotalmounting point for the 1nd1- 35 of the principal features of inventioncater arm 8. The lower end of the indicator arm is that I have devisedan instrument and asso 8 terminates in a point directly over the graphl3,

ciated par s whereby it is possible to indicate and the construction ofwhich Shall be explained hereinafter. The u er semi-circular rtion i6 40read therefrom, the percent relative humidity of pp po t of theindicator arm 8 extends over the stem of 40 the atmosphere directly fromthe instrument the bulb thermometer and is provided on Without thenecessity of referring to any extra-n6" the circumference with atransparent celluloid ous parts such as graphs or tables which requireportion FL The celluloid portion n is furth r calculations often beyondthe understanding of provided with a hair line 3 the radius of whichthose attempting to use the instrument is dependent on the position oithe 100% line on 45 A furt er feature of y invention lies in the graph[3 and therefore may be varied accordinga that y instrument y beOperated either 1y. It is necessary, however, that the orifice I is a y0 mechanically in Co o wi on the centre line of the hair line Hi. Theupper r COI1 pp s Whereby the Percent portion of extension [9 of theindicator arm 8 relative humidity of a room or building is at allextends over the stem of the Wet bulb ther- 50 times positively andimmediately controllable. mometer 2 and is provided with a transparentOther novel and important features of my incelluloid portion 20. Thehair line 2|, which tion will be apparent from the following descripisalso provided in the celluloid portion 20, is tion and accompanyingdrawing in Which: also on the centre line of the orifice I.

Fig. 1 is a front view of my invention with the In order to minimize thecost of instru- 55 ments for ordinary commercial use the L-shaped member3 may be mounted on the rod 5 by any of the known methods in order thatit may slide freely upwardly or downwardly and at the same time heldfirmly when the desired position is reached. I prefer to use a frictionspring (not shown) for this purpose. For more costly instruments,however, where accuracy is the predominant factor, I prefer to providemeans for a very fine adjustment of the extension l9 such as by means ofthe thumb-screw 24.

The water vessel I0 may be of any preferred shape and secured to thepanel I2 in any desired manner.

The graph I3, by means of which, in conjunction with the indicator 8, itis possible to read directly the percent relative humidity of theatmosphere, is devised in the following manner:

The hair lines l8 and El are placed to contact for example the 90calibration mark of their respective scales. When the indicator 6 is inthis position. of course, it will be apparent that there can be noevaporation, therefore the indicator establishes a point on the 100%curve. It should be apparent that the curve denoting the 108% relativehumidity will be a straight line passing through the point soestablished. The indicator 8 is now deflected to the left 1 by rotationon the pivotal point i, thusestablishing a second point which is alsomarked. The indicator arm 3 is again deflected to the .cft one degree ata time, or progressively increasing difference of 1 until it has coveredthe complete range. The pivot point i is then moved downwardly 10 andthe hair lines l8 and 2! adjusted to contact the calibration mark ontheir respective scales. ii is again deflected to the left one degree ata time until it has again covered the desired range, thus establishing athird point on each curve. This operation is repeated until all thepoints are established on each curve. These points, on each curve, arethen connected forming the curves as illustrated in Fig. 1.

In operation there will be a continual difference in temperature betweenthe two thermometer scales dependent on the rate of the evaporation ofthe water from the cloth enclosing the bulb iii of the wet bulbthermometer 2. The rate of evaporation varies inversely as the relativehumidity of the atmosphere, i. e. the higher the humidity the slowerwill be the rate of evaporation. ihe indicator arm 8 is so placed thatthe hair line l8 contacts the calibration mark denoting the temperaturereading of thermometer i. The indicator 8 is deflected to the left bypivoting on the point 1 until the hair line 2i contacts the calibrationmark denoting the temperature reading of thermometer 2. The indicator S-then indicates on the graph it the per cent relative humidity of theatmosphere.

It will be apparent that occasionally during the operating life of myinstrument one or other of the thermometers l and 2 may be inadvertent1y broken. In such a case it may be very difficult to replace the brokenthermometer with one whose calibration marks are directly in line withthe calibration marks of the other thermometer without going to theexpense of providing very costly precision thermometers.

In originally constructing the device, therefore, I mark the panel l2approximate to each of the thermometer stems with one or morecalibration marks, preferably every 10 degrees corresponding to thescale for which the graph is constructed.

The indicator- I further mount each of the thermometers on movable bases22 and 22a in such a manner that each of the thermometer stems may bemoved individually upwardly or downwardly by rotation of the thumbscrews 23 and 23a. In this manner it is possible to use any pair ofthermometers whose scales are approximate to the graph scale.

I have found my instrument to be particularly adapted for use inconjunction with air conditioning equipment whereby it is possible tomaintain the percent relative humidity of the atmosphere within a roomor building most suitable to the occupants or to the type of manufacturebeing carried on and, at the same time, effect the most economicaloperation of the air conditioning apparatus. I have illustrated in thedrawing a comfort zone which is readily adaptable to meet desiredconditions, either for particular types of manufacture or the occupants,and by means of which anyone operating the instrument can readilydetermine whether or not the percent relative humidity is within thedesired range. In this respect for the ordinary domestic airconditioning installations it may be necessary to show on the graph onlythis comfort zone as the average householder will not be interested inthe percent relative humidity outside that zone.

As a further feature for the more accurate determination of the percentrelative humidity I provide a blower 25 mounted in a housing 26* 27 forcirculating air at room temperature in contact with the thermometerbulbs Hi and I5. I have found that embodying this feature greatlyincreases the accuracy of my instrument while the increased cost isnegligible. The blower may be operated, such as by clockwork for aminute or so prior to taking the reading thereby ensuring that eachthermometer indicates the actual room temperature which I have found tobe as much as several degrees different from that indicated prior tooperating the blower.

Having thus fully described my invention what I claim as new and desireto secure by Letters Patent is:

1. A direct reading hygrometer which comprises a dry bulb thermometerand a wet bulb thermometer, a cross member mounted between saidthermometers on a vertically adjustable pivot supporting member, saidcross meinher being a unitary rigid structure having two arms forco-operation with the two thermometer columns and an angularly disposedpointer ad-- justable, upon corresponding adjustments of said arms, overa chart calibrated in percent relative humidity, the dry bulbthermometer arm of said cross member having an elevated arcuate portionrelative to said pivot point for registra tion with its thermometer andthe wet bulb thermometer arm extending on a line with said pivot point,the extent of the movement of said pointer across said'chart beingrelative to the difference in the temperature readings of the twothermometers.

2. A direct reading hygrometer which comprises a dry bulb thermometerand a wet bulb thermometer, a cross member mounted between saidthermometers on a vertically adjustable pivot supporting member, saidcross member being a unitary rigid structure having two arms forco-operation with and overlying the two thermometer columns and anangularly disposed pointer adjustable, upon corresponding adjustments ofsaid arms, over a chart calibrated in percent relative humidity, the drybulb thermometer arm of said cross member having an elevated arcuateportion relative to said pivot point for registration with itsthermometer and the wet bulb thermometer arm extending on a line withsaid pivot point, the extent of the movement of said pointer across saidchart being relative to the difference in the temperature readings ofthe two thermometers.

3. A direct reading hygrometer which comprises a dry bulb and a wet bulbthermometer, a cross member mounted between said thermometers on avertically adjustable pivot supporting member, said cross member being aunitary rigid structure having two arms for co-operation with andoverlying the two thermometer columns and an angularly disposed pointeradjustable, upon corresponding adjustments of said arms, over a chartcalibrated in percent relative humidity, the dry bulb thermometer arm ofsaid cross member having an elevated arouate portion relative to saidpivot point for registration with its thermometer, the wet bulbthermometer arm extending on a line with said pivot point and each armbeing provided with a window and hair lines to facilitate registeringadjustment, the extent of the movement of said pointer across said chartbeing relative to the difierence in the temperature readings of the twothermometers.

JAMES CARTWRIGHT BARNES.

